Differentiation and subsequent development of the gut represents an important clinical topic but one that is, to date, poorly understood. Sets of genes are turned on or off in an ordered and synchronized pattern as the intestine evolves from an undifferentiated endoderm into its adult differentiated form; these changes in gene expression are mediated primarily by the activation or repression of gene transcription. Our previous findings have identified the terminally- differentiated neurotensin (NT) gene (designated NT/N) as an excellent molecular model to delineate the complex cellular mechanisms regulating the region-specific patterns of expression which lead to differentiation and specialized function. We have shown that NT/N expression is developmentally regulated in a distinctive temporal- and spatial- specific pattern; NT/N expression is initially low in the fetus but rapidly increases after birth to assume the distinctive adult topographical distribution with increasing NT/N expression along the longitudinal axis of the small bowel. In the human colon, NT/N is transiently expressed in the fetus but is repressed in the adult; however, NT/N is reexpressed in certain colon cancers. The central hypothesis of our proposal continues to be that the strict expression pattern of NT/N in the gut is regulated by mechanisms which involve mainly transcriptional regulation. To examine this hypothesis we have panned experiments with the following SPECIFIC AIMS: (l) We will further define the factors regulating the developmental pattern of NT/N expression in the gut. (2) We will determine the mechanisms leading to ectopic NT/N expression in colon cancers. (3) We will characterize the age-related alterations of NT/N expression and NT-mediated growth in the gut. (4) We will analyze in vivo the NT/N regulatory elements required for the strict expression pattern in the gut. To achieve this goal, we will develop transgenic lines with the human NT/N regulatory region linked to a reporter gene to determine the elements that are required to recapitulate the normal developmental pattern of NT/N expression. The ultimate goal of our studies is to define the molecular mechanisms regulating NT/N expression in vivo. Understanding the protein-DNA interactions that are required for restricting NT/N expression will yield important information on the regulation and attainment of the differentiated gut phenotype. In addition, analysis of these cellular processes will provide a better understanding of not only normal gut development and function but may also provide a model to better elucidate the cellular events leading to gut neoplasia.